This invention relates to signal processors for extracting pertinent information about signals from a source in the presence of undesirable noise. More specifically, the invention relates to simultaneous extraction of bearing and frequency information of an acoustical signal in the presence of undesirable ambient noise.
Operational characteristics require that the prime functions of an acoustic intercept receiver are to detect, localize, and process or analyze all acoustic signals from active sonars operating in the vicinity of a submarine platform. Generally, localization comprises direction finding, i.e., determining the bearing or the angle of azimuth at which the intercepted signal arrives; and processing or analyzing, i.e., determining the frequency spectrum of the intercepted signal. The bearing and frequency information of the intercepted acoustic signal thus helps to pinpoint the movements of a moving body around a submarine. To date, all acoustic intercept receivers have used independent techniques for extracting the bearing information and the frequency information. One disadvantage of using such independent techniques is that the performance of each independent technique depends upon the characteristics of the intercepted signals and the ambient background noise. Consequently, it has been possible to obtain either the frequency information only or the bearing information only. One such attempt is discussed in U.S. Pat. No. 3,176,262 to Ehrlich et al, wherein a multimode sonar transducer, a right cylindrical hydrophone divided into four quadrants, generates four electrical signals, one signal from each quadrant, which can be represented as follows: ##EQU1## where S(.phi.,t) is the acoustic signal arriving from a source at a direction angle .phi.,
R(f) is the omnidirectional receiving sensitivity, PA1 C(f) is the circumferential receiving sensitivity, PA1 S(.phi.,t) is a time varying, plane-wave, acoustic signal from a source at a direction angle .phi., and .phi. is the direction angle, i.e., the angle of azimuth of the source of the acoustic signal.
These four signals are combined in a sum and difference network to obtain three signals: ##EQU2##
These three signals have been processed to extract the bearing information as discussed in the Ehrlich et al patent.
Using the prior art methods, it has been possible to obtain either the frequency information only or the bearing information only.